Such methods may especially be used in the manufacture of sensors, e.g. capacitive ceramic pressure sensors, in order to obtain electrically conductive connections between a conductive sensor shield or a connection between the sensor and measurement electronics or a reference potential.
One example of a capacitive ceramic pressure sensor is described in German Patent, DE 10 2008 054 879 A1. It comprises a ceramic base body, a pressure-sensitive measuring membrane connected to the base body forming a measuring chamber, and an electro-mechanical transducer. The electro-mechanical transducer transforms a pressure-related deformation of the measuring membrane into a primary electrical signal, which is available via ports that are led through the base body to an outer surface of the base body. Said ports are connected by connecting elements to an on-site electronic system which is separated from the base body. The electronic system generates a measuring signal from the primary signal and makes it accessible for further processing, evaluation and/or display.
European Patent, EP 1 106 982 A1 describes another example of a ceramic pressure sensor having a base body provided with a conductive coating to shield it against electromagnetic noise signals.
Today, ceramic base bodies are preferably coated by sputtering the base body with metals made available in a target, e.g. gold or silver. Alternatively, metallic varnishes such as conductive carbon or silver lacquers are used.
Such coatings have the disadvantage that they regularly have very good wetting properties as regards soft solders. This creates a risk of the soft solder material applied to it running uncontrollably across the surface of the coating during soldering, and even wetting parts of the surface of the coating outside the connection point.
If a larger area is wetted, there will be less solder material available per unit area. In order to obtain a qualitatively unobjectionable solder joint, it is necessary to use amounts of soft solder material large enough to ensure that there will always be a sufficient amount of solder material per unit area at the connection point, despite the flow process initiated during the soldering process.
After soldering, the solder material solidifies throughout the wetting area. This means that uneven areas may occur on the coating surface even outside the connecting point. In many cases areas affected by this cannot therefore be used, or if so only to a limited extent. Due to the unevenness, these areas cannot be used, for example, to support a sensor bracket, fixing or mount. The latter are, for instance, required for installing the sensor in a housing, for mounting it at its location of use or for installing it in a process interface. Furthermore, other elements, such as a drilled hole in the base body provided for inputting a reference pressure, must be placed at a suitable minimum distance from the connection point. Both aspects are disadvantageous, particularly with regard to the miniaturization of sensors which is desired for many applications.
In order to limit the surface wetted during soft-soldering, it would be possible to apply an additional coating of non-wettable material to the surface area of the coating surrounding the connection point. However, this would require an additional process step.
In cases where this is possible due to the other requirements made of the coating, the coating might be interrupted in the area surrounding the connection point in question. This could, for example, be done by applying an appropriate mask during the coating process.